Sound reproducing apparatus



March 27, 1934.

J. c. DOUW 1,952,539-

SOUND REPRODUCING APPARATUS Filed Dec 26, 1929 DOLLW Patented Mar. 27, 1934 UNITED STATES PATENT OFFICE soUND asmonucma APPARATUS J. C. Douws Patents Application December 26, 1929, Serial No. 416,662 In the Netherlands July 26, 1929 3 Claims. (01. 181-31) The invention relates to apparatus for the reproduction of sound in which the sound vibrations are transmitted to the air by means of a diaphragm having a relatively large surface. such apparatus a screen plate is in most cases used for the'improvement of the reproduction of the lower notes by preventing a short-circuit of the air vibrations around the edge of the diaphragm. The screen plate is usually arranged '10 in such amanner that it is joined to the free edge of the diaphragm which may be of cone or other shape.

Experience has shown that the reproduction of sound by apparatus mentioned may be considerably improved if the diaphragm and the screen plate are not joined directly together but are separated by an intermediate member having an increasing cross section.

According to this invention, there is provided an apparatus for the reproduction of sound having a diaphragm of relatively large surface and a screen plate wherein the screen plate is separated from the diaphragm by a funnel shaped member or similar sound channel which is joined at one end to the edge of the diaphragm and at the other end to an opening provided in the screen plate.

The advantage which is attained by the construction of apparatus according, to this invention is that a more uniform reproduction of all notes is obtained. This appears from the fact that the various vibrations are distinguishable by the hearer more clearly from one another and produce a more natural impression than the sound produced by the forms of apparatus hitherto used.

This advantage can be further increased by arranging a conical shaped member co-axially 0 within the funnel shaped member so as to be supported thereby. When a conical shaped diaphragm is used in the apparatus, the apices of With of sound, and is illustrated partly in section and partly in elevation.

The drawing shows a screen plate 1 which is not arranged directly round the cone-shaped diaphragm 7 of a loundspeaker 6, but is separated from it by an intermediate member 2 in the form of a truncated cone.- The member 2 forms a channel for the transmission of sound from the diaphragm 7 to the outer air. The funnel shaped member is provided at the wider end thereof with a flange 3 which is secured to the screen plate 1. The dimensions of the member 2 at the narrow end thereof are substantially equal to those of the conical shaped diaphragm 7. The member 2 is disposed between the screen plate 1 and a stiifening plate 4 which are connected together by a series of supports 5. The stiffening plate 4 is connected in any desired manner to the frame 11 of the loudspeaker 6, which, with the exception of a portion which is broken away, is shown in elevation in the drawing.

The edge of the diaphragm '7 is supported by the frame 11 of the loud speaker and a ring 12 of felt or other suitable material may be clamped between theframe 11- and the stiffening plate 4 so as to prevent leakage of air pressure between the diaphragm '7 and the cone shaped member 2.

Aconical shaped hollow body 8 is arranged coaxially within the member 2 and is secured thereto, by means of a number of distance pieces 9 which transmit the vibrations created in the body. 8 to the said member 2. The apex of the hollow body 8 is strengthened, for example, by arranging therein a correspondingly shaped piece of wood 10 which is held in position by means of a screw or other fastening device. The screw bears against a metal cap applied exteriorly of the apex. of the body 8.

The funnel shaped member 2 and the hollow body 8, are preferably made of a sheet of wood which is maintained under tension by layers of flexible material 9 and 10', respectively, aflixed thereto and thus has no tendency to develop resis of approximately the same size as that of the diaphragm.

The construction of the apparatus which drives the diaphragm forms no part of this invention. It is to be understood that the screen plate with the intermediate funnel shaped member secured thereto and assembled with the hollow body 8 may be placed on the market without the loudspeaker unit.

What I claim is:

1. The combination with a sound reproducing device having a diaphragm of relatively large area, of a screen plate separated therefrom and having an opening therein, a truncated coneshaped member having its minor end in proximity to the diaphragm and its major end-connected with the plate and coinciding with the opening thereof, and a conical shaped body supported axially within said member and annularly spaced 

